A prohibition of equilibrium spin currents in multi-terminal ballistic devices

We show that in the multi-terminal ballistic devices with intrinsic spin-orbit interaction connected to normal metal contacts there are no equilibrium spin currents present at any given electron energy. Obviously, this statement holds also after the integration over all occupied states. Based on the proof of this fact, a number of scenarios involving nonequilibrium spin currents is identified and further analyzed. In particular, it is shown that an arbitrary two-terminal device cannot polarize transient current. The same is true for the output terminal of an N-terminal device when all N-1 inputs are connected in parallel.Comment: 3 pages, 1 figure; presented at the DARPA SPinS review (#Th-19), San Francisco, CA, October 25-28, 200

Break-down of the density-of-states description of scanning tunneling spectroscopy in supported metal clusters

Low-temperature scanning tunneling spectroscopy allows to probe the electronic properties of clusters at surfaces with unprecedented accuracy. By means of quantum transport theory, using realistic tunneling tips, we obtain conductance curves which considerably deviate from the cluster's density of states. Our study explains the remarkably small number of peaks in the conductance spectra observed in recent experiments. We demonstrate that the unambiguous characterization of the states on the supported clusters can be achieved with energy-resolved images, obtained from a theoretical analysis which mimics the experimental imaging procedure.Comment: 5 pages, 3 figure

Skrining Fitokimia Minuman Tradisional Moke dan Sopi sebagai Kandidat Antimikroba

Sopi and moke of East Nusa Tenggara Province are some traditional beverage made from nira or interest leads palm (Borassus flabellifer L.). Several studies have shown that sopi and moke have an antimicrobial activity. Antimicrobial activity of plants derivatives may be influenced by the content of phytochemical compounds. The purpose of this study was to determine the class of phytochemical compounds in sopi and moke. Phytochemical testing performed on seven chemical compounds, namely alkaloids, flavonoids, phenols hydroquinone, steroids, triterphenoid, tannins and saponins. The results show that sopi contains of alkaloids and moke contains of phenol hydroquinone and saponins. Antimicrobial activity of sopi and moke supposed to be caused by these three compounds and this could be a potential source of an alternative disinfectant candidate

Electron Transport Through Molecules: Self-consistent and Non-self-consistent Approaches

A self-consistent method for calculating electron transport through a molecular device is proposed. It is based on density functional theory electronic structure calculations under periodic boundary conditions and implemented in the framework of the nonequilibrium Green function approach. To avoid the substantial computational cost in finding the I-V characteristic of large systems, we also develop an approximate but much more efficient non-self-consistent method. Here the change in effective potential in the device region caused by a bias is approximated by the main features of the voltage drop. As applications, the I-V curves of a carbon chain and an aluminum chain sandwiched between two aluminum electrodes are calculated -- two systems in which the voltage drops very differently. By comparing to the self-consistent results, we show that this non-self-consistent approach works well and can give quantitatively good results.Comment: 11 pages, 10 figure

Microscopic non-equilibrium theory of quantum well solar cells

We present a microscopic theory of bipolar quantum well structures in the photovoltaic regime, based on the non-equilibrium Green's function formalism for a multi band tight binding Hamiltonian. The quantum kinetic equations for the single particle Green's functions of electrons and holes are self-consistently coupled to Poisson's equation, including inter-carrier scattering on the Hartree level. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self consistent Born approximation of the scattering self energies. Photogeneration of carriers is described on the same level in terms of a self energy derived from the standard dipole approximation of the electron-photon interaction. Results from a simple two band model are shown for the local density of states, spectral response, current spectrum, and current-voltage characteristics for generic single quantum well systems.Comment: 10 pages, 6 figures; corrected typos, changed caption Fig. 1, replaced Fig.

Electron Transport Through Molecules: Gate Induced Polarization and Potential Shift

We analyze the effect of a gate on the conductance of molecules by separately evaluating the gate-induced polarization and the potential shift of the molecule relative to the leads. The calculations use ab initio density functional theory combined with a Green function method for electron transport. For a general view, we study several systems: (1) atomic chains of C or Al sandwiched between Al electrodes, (2) a benzene molecule between Au leads, and (3) (9,0) and (5,5) carbon nanotubes. We find that the polarization effect is small because of screening, while the effect of the potential shift is significant, providing a mechanism for single-molecule transistors.Comment: 4 pages, 4 figure

Coherent Transport through an interacting double quantum dot: Beyond sequential tunneling

Various causes for negative differential conductance in transport through an interacting double quantum dot are investigated. Particular focus is given to the interplay between the renormalization of the energy levels due to the coupling to the leads and the decoherence of the states. The calculations are performed within a basis of many-particle eigenstates and we consider the dynamics given by the von Neumann-equation taking into account also processes beyond sequential tunneling. A systematic comparison between the levels of approximation and also with different formalisms is performed. It is found that the current is qualitatively well described by sequential processes as long as the temperature is larger than the level broadening induced by the contacts.Comment: 11 pages, 5 figures included in tex

Hund's rule and metallic ferromagnetism

We study tight-binding models of itinerant electrons in two different bands, with effective on-site interactions expressing Coulomb repulsion and Hund's rule. We prove that, for sufficiently large on-site exchange anisotropy, all ground states show metallic ferromagnetism: They exhibit a macroscopic magnetization, a macroscopic fraction of the electrons is spatially delocalized, and there is no energy gap for kinetic excitations.Comment: 17 page